No he's not the greatest.
He's a great manager, I will give you that, but he's not the GOAT. For me, Fergie will always be that and not just because he's been our manager.
Fergie managed to take a shit club like Aberdeen to a European Cup.
Fergie managed to bring United up to the best club in the world when it was utter shite and getting its arse kicked by Liverpool for a decade.
Fergie never had or walked into a club that had unlimited resources and world class players. Everything he did was done from scratch.
Pep, on the other hand, has walked into top clubs from the start, Bayern, Barcelona, City, where funds and players have been there before he came.
Sure, he's done great while he's been there, but there's a world of difference between having the skills to take Aberdeen to a Euro Cup and prime Barca.
When Pep joins Kilmarnock or St. Mirror and wins a Euro cup, then I'll gladly admit he's the best. Until then, no chance.